Transactions . ent. They cannot be, of course, regardedas very serviceable criteria in determining the molecular natureof the process; but they are frequently so characteristic a featurethat they will lead one to look for other criteria of a more certaincharacter. It is important that they should not be confused with inter-spaces l^etween crustified layers which line cavities. Whenmineral crusts are very definite there is usually no difficulty; butwhen crustified layers are imperfectly formed the relation of theopc-nings to fragments of country rock should be olume vuggs are nuich
Transactions . ent. They cannot be, of course, regardedas very serviceable criteria in determining the molecular natureof the process; but they are frequently so characteristic a featurethat they will lead one to look for other criteria of a more certaincharacter. It is important that they should not be confused with inter-spaces l^etween crustified layers which line cavities. Whenmineral crusts are very definite there is usually no difficulty; butwhen crustified layers are imperfectly formed the relation of theopc-nings to fragments of country rock should be olume vuggs are nuich more irregular in shape than cavity vug<j:s,are rarely if ever angular in outline, are generally more intricateand bear much less definite relations to wall rock, included frag-ments, etc., and are usually more widely disseminated in an oremuss. In some instances the distinction is difficult to make criterion then fails; but in the majority of cases the origin ofthe openings is at once evident. ^ w. 1 !».. IWi*-! liilii- lialuial .-Ua . .^liait ly nplacctiKHt of altrriiatiiiK (ioloriiit*- anill»uinl> **>»luniinou> UTOllS •*hnl« Replacement Ore Bodies—Irving 469 9. Excess of Volume of New Mineral Over Pore Space of Country Rock. In many dense iirneous rocks it frequently happens thatdisseminated particles of ore are introduced in the vicinity or opening. It may be an easy matter to determinewhether they are epigenetic or igneous in origin; but the dis-tinction between impregnations, , particles of ore deposited inoriginal pore space, and disseminated replacements is more diffi-cult. In such cases, if the average porosity of the country rock l^edetermined and then the total volume of the new mineral bedetermined, if the volume of the new mineral is in excess of theavailable pore space some of the rock matter must have beenremoved to make room for it. Th
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Keywords: ., book, bookcentury1800, booksubjectmineralindustries, bookyear1895
